Cloud

A recent study reveals that trees have a natural way of seeding clouds in the atmosphere. The findings from the two experiments posted in Nature and Science journals reveal that trees release molecules that contribute in cloud seeding. It was first thought that the pollutant Sulfuric acid is required for a particular cloud formation, but with the recent findings, the perception of modern scientists towards the cloud cover condition during the pre-industrial period will change.

Reto Knutti, a climate modeller at the Swiss Federal Institute of Technology (ETH Zurich) said that the predictions for future climate change would have to consider the results of the recent experiments. Knutti said that there has been a huge uncertainty with regards to the effects of man-made emissions to the atmosphere, particularly in shaping up the clouds.

The advent of the industrial period featured the burning fossil fuels, which indirectly produces carbon dioxide and Sulfuric acid. The latter is a known component of cloud seeding, therefore climate scientists have assumed a large increase in cloud cover in the beginning of industrial period, which is thought to have an overall cooling effect by reflecting sunlight back into space.

While the burning of fossil fuels produces carbon dioxide which is a primary cause of Greenhouse effect, the emission of Sulfuric acid into the atmosphere may have masked the negative effects of industrial processes as Sulfuric acid contributes to a thicker cloud cover.

Atmospheric scientists thought that only Sulfuric acid vapor could trigger cloud formation. As a result, it was thought that pre-industrial skies were somewhat less cloudy than present ones because they contained less of this pollutant, says Jasper Kirkby, a physicist at the CERN.

However, Kirkby noted that it is still too early to be certain whether this is true in practice or by extent this theory could be true, as there are so many factors come into play. “There are many uncertainties; we are only talking about one,” he said.

To confirm the cloud seeding process, Kirby turned to the Cosmics Leaving Outdoor Droplets (CLOUD) experiment that he founded. CLOUD is a three-meter tall stainless steel tank that can simulate a vast range of atmospheric conditions, and it can be hooked up to the beams of particles that feed the Large Hadron Collider (LHC) at CERN. The LHC simulates the effects of cosmic rays in the atmosphere. Cosmic rays are high-energy subatomic particles that come from outside the Solar System and are thought to contribute in cloud formation.

Kirkby and his co-authors report that aerosols can form and grow to the size needed to seed a cloud from the molecules naturally emitted by trees without requiring Sulfuric acid. To note, water vapor in the atmosphere cannot simply transform into a cloud. Aerosols are required for the vapor to become more condensed and form clouds.

In these experiments, the team used α-pinene, a molecule that helps to give fir forests their characteristic smell. However, compounds from other types of vegetation might have a similar effect.

Bjorn Stevens, atmospheric scientist from the Max Planck Institute for Meteorology in Hamburg, Germany, said that the findings of the experiments have another important implication regarding the public’s perception of global warming and clean air. Some scientists believe that measures such as ridding the atmosphere of Sulphur dioxide by limiting coal plant processes could remove some of the beneficial cooling effect of clouds, and therefore boost global warming. However, upon knowing that trees can do the cloud seeding job themselves, this will be less of a concern today.

“What it means is, we don’t have to fear clean air,” says Stevens.